To change the terms used by Rooms for you can use admin/rooms/config/terminology.

Rooms terminology tries to strike a balance between the generic and useful enough to get you started quickly. This means that in certain places users will see words like “Units” which might not make a lot of sense. At admin/rooms/config/terminology you can now change all user-facing terminology quite easily. Keep in mind that for some instances you will need to clear cache to see the changes. This will work also for transltions using the i18n Drupal module - https://www.drupal.org/project/i18n